1. Field of the Invention
The present invention relates to an apparatus for and a method of measuring the image qualities of a color display unit such as a color television receiver, a television color cathode-ray tube, a display monitor (a color cathode-ray tube as a computer display monitor), a projection display unit, or the like.
2. Description of the Prior Art
One conventional apparatus for measuring the image qualities of a color display unit will be described below with reference to FIG. 1 of the accompanying drawings. In FIG. 1, the color display unit, denoted by 1, whose image qualities are to be measured by the apparatus comprises a color television receiver which has a color cathode-ray tube. However, the color display unit 1 may comprise a television color cathode-ray tube, a display monitor (a color cathode-ray tube as a computer display monitor), a projection display unit, or the like.
The apparatus has a color video camera 2 for imaging images in their entirety which are displayed on the color display unit 1 and a fixed-focus lens 2L used as an imaging lens of the color video camera 2. The color video camera 2 and the fixed-focus lens 2L jointly serve as an image quality sensor (color image quality sensor).
A video monitor 7V, which comprises a television color cathode-ray tube, is supplied with an image signal from the color video camera 2, and displays on its display screen an image of the display screen of the color television receiver as the color display unit 1.
An image processing circuit 5 has an A/D converter 5A for converting an image signal from the color video camera 2 into a digital image signal, and a frame memory 5B for storing the digital image signal from the A/D converter 5A. If a digital image signal is directly generated by the color video camera 2, then the A/D converter 5A of the image processing circuit 5 may be dispensed with. The digital image signal (digital image data) read from the frame memory 5B is transferred through a bus line (two thin wires) to a memory (not shown) in a CPU (central processing unit) as a computer, the CPU having a ROM which stores a program and a RAM for storing processed data.
A monitor 7, which comprises a color cathode-ray tube for use as a computer display monitor, is connected to the CPU 6.
The CPU 6 controls a signal generator 12 through a bus line for generating an image signal such as a pattern signal which is necessary for measurement. The generated image signal is supplied to the color display unit 1 for displaying a pattern image necessary for measurement on the display screen of the color cathode-ray tube.
For example, if image distortions (geometric raster distortions) of an image are to be measured, then the CPU 6 calculates the position of the image from the image data, and displays calculated positional data as graphic data or numerical data on the display screen of the monitor 7 on a real-time basis. The CPU 6 may store the calculated positional data in an external memory such as a hard disk (not shown) or transmit the calculated positional data through a network to a host computer for analytical processing or the like.
An input/output interface circuit 9, which is connected to the CPU 6, is used to control measurement start and end signals that are used in the measurement of image qualities on a display unit production line, or to generate serial control signals that are used in the automatic adjustment of the image qualities of the color display unit 1.
FIG. 2 of the accompanying drawings shows another conventional apparatus for measuring the image qualities of a color display unit. The conventional apparatus shown in FIG. 2 is similar to the conventional apparatus shown in FIG. 1 except that a common monitor 7K is used in place of the monitors 7, 7V shown in FIG. 1.
In the conventional apparatus shown in FIG. 2, the common monitor 7K has a variable scanning frequency. The scanning frequency of the common monitor 7K at the time an image signal from the color video camera 2 is supplied to the common monitor 7K differs from the scanning frequency thereof at the time a display signal based on measured image qualities from the CPU 6 is supplied to the common monitor 7K.
The conventional apparatus shown in FIG. 1 uses two monitors and hence requires more complex hardware than the conventional apparatus shown in FIG. 2.
As described above, the conventional apparatus shown in FIG. 2 uses the common monitor 7K whose scanning frequency at the time an image signal from the color video camera 2 is supplied to the common monitor 7K differs from the scanning frequency thereof at the time a display signal based on measured image qualities from the CPU 6 is supplied to the common monitor 7K. The common monitor 7K with the variable scanning frequency is more expensive than the monitors 7, 7v, and hence the conventional apparatus shown in FIG. 2 is relatively expensive to manufacture.
The conventional apparatus have no means for assisting the operator to determine a field of view of the color video camera 2 when the operator adjusts the position of the color video camera 2 while viewing an image displayed on the display screen of the color display unit 1. Consequently, the operator needs to be experienced enough to establish a field of view of the color video camera 2.